Stoker driving arrangement



Feb. 18, 1941. w. o. LUM

STOKER DRIVING ARRANGEMENT Filed Nov. 16, 1959 3 Sheets-Sheet lInventor: Walter O. Lurn,

W MM ttorneg.

His

Feb. 18, 1941. w. o. LUM 2,232,545

STOKE]! DRIVING ARRANGEMENT Filed Nov. 16, 1939 3 Sheets-Sheet Fig. 12.

Inventor: Walter O. Lum,

His Attofneg.

Feb. 18,1941. UM 2,232,545

STOKER DRIVING ARRANGEMENT Filed Nov. 16, 1939 3 Sheets-Sheet 5Ihventof: Walter O. Lum,

bag 2 His ttorneg.

Patented Feb. 18, i941 UNITED STATES STOKER DRIVING ARRANGEMENT Walter0. Lum, West Orange, N. J., assignor to General Electric Company, acorporation of New York Application November 16, 1939, Serial No.304,754

15 Claims.

This invention relates generally to operating mechanisms for materialconveying systems and more particularly for screw type coal conveyors ofa furnace-stoker arrangement.

6 Material conveying systems such as mechanical fuel stokers areliable'to become clogged for various reasons such as by congestion ofthe material, or by large pieces of coal, pieces of metal or otherforeign material becoming caught between the screw and the edges of thehopper opening, resulting in the stalling of the driving motor. Meansare usually provided in the driving connection between the motor and theconveyor screw to automatically sever the connection or to deenergizethe motor upon the occurrence, of a .predetermined overload condition.Each time the motor becomes stalled and disconnected by reason of theconveyor becoming jammed, it is necessary for a person to investigatethe cause of the difficulty and to clear away the obstruction before themotor may be reset for the continuation of operation. This procedureinvolves more or less manual labor, is expensive and generallyunsatisfactory. In the majority of instances, the jammed condition ofthe conveyor may be rectified by temporarily reversing the direction ofoperation of the motor and subsequently operating it forward again. Ifnecessary, the reversal of the motor may be repeated several times untilthe passage becomes clear and free of the obstruction. It is thereforethe principal object of this invention to providea driving mechanism fora material conveying system which is automatically controlled upon theoccurrence of a clogged condition of the conveyor system for temporarilyreversing the direction of operation of the driving motor, whichoperation is repeated until the conveyor is free of the ob structioncausing its clogging. Further objects and advantages of my inventionwill become apparent as the following description proceeds, and thefeatures of novelty which characterize my invention will be pointed outwith greater particularity in the claims annexed hereto and forming apart of this specification. v

For a better understanding of my invention,

reference may be had to the accompanying drawings in which Fig. 1represents a furnace equipped with a stoker mechanism and driving meanstherefor; Figs. 2 and 3 are enlarged views partly in section of a torqueresponsive coupling arranged between the motor and stoker shown in Fig.1; Figs. 4 and 5 are views similar to Figs. 2

and 3, respectively, showing the coupling ina sec- 0nd operativeposition; Fig. 6 is a schematic cir cuit diagram illustrating a controlscheme for the motor of Fig. 1; Fig. 7 illustrates a second embodimentof the invention in which a different and particular type of motor issubstituted for 5 that shown in Fig. 1; Figs. 8, 9 and 10 illustratevarious positions of the mechanical control means for the motorillustrated in Fig. 7; Fig. llis a schematic circuit diagram for thecontrol of the motor shown in Fig. 7; and Fig. 12 is a schematic l0diagram illustrating an automatic timing mechanism for use in connectionwith either modification.

Referring now to Fig. l of the drawings, I0 is a furnace having afirepot II arranged in the 15 lower portion thereof to which fuel is fedby means of a suitable stoker or conveyor screw I2 from a storage bin orhopper l3. A suitable motor I4 having a speed reduction gearing I5 iscoupled through a torque responsive device It to 20 the shaft ll of theconveyor screw. The motor I4 is of a reversible type, as will be morefully described hereinafter, and is adapted for driving the conveyorscrew in the forward direction to advance fuel from the bin I3 to thefirepot II 25 Upon the conveyor screw I2 becoming clogged or stalled forany reason, such as by a large lump of coal getting caught at the' inletthereto, the torque responsive device I6 will effect the reversal of theconnection to the motor I 4 to reverse the 30 rotation of the screw fora predetermined period of time. The period of reverse operation of themotor is limited to merely one or two revolutions of the conveyor screwI2 so as not to feed live coals from the firepot II into the storage binI3, 35 Subsequent to the period of reverse operation, the motor I4 willbe automatically reconnected for operation in the forward directionagainand after a number of such reversals the congestion causing the stallingwill be cleared away, or the 4 large lump of coal willbe broken up andthe advancement of fuel will continue in the regular manner.

Referring now to Figs. 2 and 3, the details of the torque responsivedevice I6 will be described. 5 This device comprises a pair of similardisks 30 and 3|, disk 30 being keyed to the motor drivin shaft whiledisk 3| is keyed to the driven or conveyor shaft I1. A portion of disk3| is broken away for the purpose of more clearly illustrating 50 thestructure of the facing surfaces of the cooperating disks. A number ofsuitably spaced apart lugs 32 are integral with the peripheral"portion'of the disk 39. A similar number of similarly spaced apart lugs33 are provided integral with the adjacent face of the disk 3i. Springs33 are arranged between the lugs 33 and 33 to maintain the backs of thepairs of adjacent lugs of the two disks in an abutting relationship asshown. Assuming now that the coupling is being driven'in the fueladvancing direction, or counterclockwise, and that the conveyor screw l2operating in the forward direction becomes clogged creating" apredetermined abnormal increased resistance to rotation of the drivendisk 3|, due to an increase in torque applied to the driving disk 33 bythe motor, the springs 34 will be compressed and the normally abuttinglugs 33 and 33 will be separated, as indicated more clearly in Fig. 4.This relative angular displacement of the disks 33 and 3| from theirnormal relationship will cause the cams 33, which are integral with disk33, to engage with the plungers 33, which are slidably mounted inbushings 31 secured to disk 3|, to force the plungers to the rightagainst the collar 33. The collar 33 is normally biased to the left bymeans of a spring 33 arranged between the collar 33 and a stop 43 fixedto the shaft II. The collar 33 being axially movable upon the shaft II,when engaged by-the end of the plunger 33, will be forced to the rightto pivot the engaging circuit controller lever ll in thecounterclockwise direction against the force of the biasing spring 42 asshown in Fig. 5. The upper end of the controller lever ll is looselyconnected to the overcenter snap acting switch arm 44 and upon actuationof the lever 4|, the switch 34 is thrown over to its secondoperativeposition, disengaging the fixed contact 43 and engaging fixedcontact 43. Connected to the lever ll is a suitable time delay device Iwhich retains the lever ll in the operated position, illustrated in Fig.5, for a predetermined length of time after which the lever 4| isreturned to its normal position, as indicated in Fig. 2, by the biasingspring 42. It is understood that immediately following the initialoperation of the lever 4|, the motor connections are reversed whereuponthe conveyor screw I2 is driven in the reversed or clockwise direction.During reverse operation of the motor the lugs 32 of the driving disk 33engage directly with the abutting faces of the lugs 33 of the drivendisk 3| and positively rotate the conveyor screw I! in the reversingdirection. It is obvious, therefore, that the collar 38 will be restoredto its normal position immediately following the reversal of the motorconnections, while the time delay device maintains the reversingconnection for the stoker motor II for a predetermined length of time,sufficient for the screw I! to make one or two complete revolutions inthe backward direction.

Referring now 'to Fig. 6, the electrical control system for the stokerdriving motor M will be described. Current may besupplied to the systemfrom a suitable alternating-current source indicated by the supply linesSI and 52. To initially energize the system the control switch 53 may beclosed, which connects the primary winding of the transformer 53directly across the supply lines. The operation of the stoker isnormally primarily controlled by means of a thrmostat 33 which may besuitably arranged within the enclosure to be heated by the furnace ID.The thermostat 55 comprises a temperature responsive bimetallic element53 which upon a predetermined low temperature condition engages with thefixed contact BI to connect the winding of relay I3 across the secondarywinding of the transformer SI. Upon the pick-up of the relay 33 aholding circuit is completed therefor through the conductors I3 and x33and contact arm 3| paralleling the thermostat element 33 and fixedcontact II. Upon a predetermined high temperature condition occurringwithin the enclosure the thermostat element 33 will bend to the leftengaging with the fixed contact 33, thereby short circuiting the relaywinding 33 causing it to drop v to the deenergized position.

Assume first that the furnace is in normal operation and that theenclosure thermostat calls for heat. The contact arm II of the relay IIestablishes a control circuit for connecting the stoker motor II foroperation in the forward direction. This circuit extends from theleft-hand terminal of the secondary winding of transformer 34 throughthe contact arm II, line 12, torque switch arm 44, fixed contact 48,winding of relay 13, to theright-hand terminal of the secondary windingof transformer 54. As the relay I3 picks up, its contact arms 14 and I!establish circuits for energizing the motor I for operation in theforward running direction. The motor will be maintained in operationuntil the demand for heat by the enclosure is satisfied, when thethermostat element 33 will engage with the fixed contact 32 to cause therelay 53 to drop out, thereby deenergizing the control relay 13. If,however, the conveyor screw I 2 becomes stalled, the torque switch 43will be operated to engage the fixed contact 43, thereby energizing therelay I3 which picks up contact arms II and 13 to establish circuits foroperating the motor ll in the reverse direction. As previouslyexplained, after a predetermined time the torque switch 44 will berestored to the normal position engaging with fixed contact 43, therebydeenergizing relay I3 and energizing relay 13 to again connect the motorH for operation in the forward direction.

The forward running circuit for the motor established by the pick-up ofrelay I3 extends from the supply line 3| through line 30, contact arm 15of the relay 13 in the energized position, line 3|, the running winding32 of the motor l3, contact arm I3 of the relay 13 in the deenergizedposition, lines 33, 34, contact arm II of relay 13, line 35, to theother supply line 32. Another circuit is established for energizing thestarting winding of the, motor I 4 extending from the supply line 5|through line 33, contactor 31 of the motor speed responsive device 33,line 33, motor starting winding 9i, capacitor 32, lines 33, 33, 33,contact arm 14 of the relay I3, line 33, to the other supply line 32. Assoon as the motor reaches approximately normal speed, the centrifugaldevice 33 will open the contacts 31 to effect the deenergization of .thestarting winding 3!. The reversing circuit for the motor established bythe pick-up of relay 13 extends from the supply line 5| through line 33,contact arm 13 of the relay 13 in its upper position, running winding 32of the motor H, .the contactor arm II of the relay I3 in its lowerposition, connection 34, line 34, contact arm II of the relay 13 in itsupper position, line 35, to the other supply line 32. The startingwinding connection is of coursenot reversed but is completed throughcontact arm II of relay I3.

In a second and preferred embodiment of my invention, I utilize aself-reversing motor in lieu of the motor ll described above. Such amotor is described in the Patent No. 2,105,514, Alfred S. Welch, issuedJanuary 18, 1938, and assigned to the General Electric Company, theassignee of the present invention. This motor has such a characteristicthat it will drive any load less than that corresponding to its pullouttorque but when it encounters a load which it,cannot carry atsynchronous speed, it immediately stops because its synchronous torqueis greater than any torque .below synchronous speed and if the motorremains energized when thus stopped by an overload in one direction, itwill immediately start up in the opposite direction. tinue to run inthis direction until it is again stalled, when it will commence torotate in the forward direction again. Referring to Fig. '2, such amotor I is shown provided with suitable speed reducing gearing in casingIll and is adapted to be fast coupled to the-fuel advancing screw shaftI1. When initially energized, the motor may start in either directionand will drive the fuel conveyor screw in either direction until it isstalled for any reason, when the motor will automatically reverse itsdirection of rotation. A ratchet means is provided for limiting therotation of the motor in the reverse direction which is more clearlyshown in the end views 0, I and I0. A ratchet disk I02 is secured to theshaft I1 andis provided with a shoulder or stop I03 facing away from thedirection of normal or forward rotation of the motor. A cooperating pawlI04 is pivoted as at I05 to the gear housing IN and is provided with atoe I06 and a heel I01. The pawl I04 is biased to either of twopositions by means of an overcenter spring I08 arranged between a studI03 and one end IIO of the pawl I04. During forward rotation of themotor, when the disk I02 is rotated in the counterclockwise direction,the pawl I04 will be merely rocked about its pivot as the tip of thestop I03 alternately strikes the heel I01 and the toe I06. Now assumethat the torque of themotor in the forward direction has beenoverpowered by the resistance of the fuel advancing screw by reason ofits having become clogged. The motor will immediately start up in theopposite or clockwise direction of rotation. Assume that'at the momentof reversal the ratchet disk and pawl are inthe relative positions inFig. 9. The disk I02 rotating clockwise will first strike the heel I01,which is riding on the edge of the disk, rocking the pawl about itspivot so that the toe I06 is moved into engagement with the disk edge bymeans of the overcenter spring I08. As the stop I03 comes around asecond time, it will engage with the toe I06 of the pawl I04. The motorthereupon will be stalled and it will immediately start up in theopposite or forward direction of rotation. The motor will continue tooperate in the forward direction until the fuel advancing screw jamsagain or until the motor is deenergized by the operation of the controlto the open circuit position. By the ratchet arrangement shown, therotation of the motor in v the reversing direction will continue, formore than one revolution and is positively limited to a maximum of twocomplete revolutions of the fuel conveyor screw.

The electrical control system for the motor just described is relativelysimple in that no opparatus is required for reversing the motorconnections. As illustrated in Fig. 11, power is adapted to be suppliedto the stoker motor from a suitable alternating-current source of supplythrough the leads I20, I2I, a suitable switch I22 being provided in theline I20 for controlling the energization of the system. Upon theclosure of switch I22, the primary winding of the transformer I23 isconnected across the supply lines,

It will conthereby energizing the enclosure thermostat I24. Theenclosure thermostat I24 is similar to the thermostat 55 and comprises abimetallic temperature responsive element I23 adapted to engage witheither of two oppositely arranged fixed contacts I21 and I28. Upon thetemperature within the enclosure dropping below a predetermined value,the element I26 will bend to the right engaging with fixed contact I28,thereby connecting the winding of relay I26 across the secondary windingof the transformer I23. Upon the pick-up of relay I 23, a holdingcircuit will be established therefor by its contactor HI and the linesI32 and I33 paralleling the thermal responsive element I26 and fixedcontact I28. Upon the pick-up of relay I28, its contactor I34 willcomplete an energizing circuit for the motor I00. The operation of themotor I00 will be continued until the demand for heat by the enclosureis satisfied, as indicated by the bending of the thermal responsiveelement I26 to the left engaging with the fixed contact I21 whichshortmatically in Fig. 12. A collar I40 may be secured to the conveyorshaft IT by means of a set screw I, the collar being provided with a camprojection I42. The cam is adapted to engage with an end I43 of a leverI44 which is pivoted as at I45 and biasedin a counterclockwise directionby means of a relatively light spring I46. The lever I44 is arranged foroperating a pawl I41 into engagement with a ratchet wheel I48 to rotateit by steps in a clockwise direction. The pawl I41 is biased against astop I49 by means of a spring I50 and is provided with a slot I5I forreceiving a pin I52 secured to the arm I44. The end of the arm I44 isprovided with a hinged tip I55 which is adapted to engage with the endof the pivoted lever I56 to carry it upwardly but not downwardly.Secured to the lever I56 is a spring pawl I51, the end of which isadapted to engage with the teeth of the ratchet disk I40 to retain it inthe actuated position as it is moved by the pawl I41. The lever I56 andspring I51 are normally biased to the inoperative position by means of aspring I50. The return of the lever I56 to the inoperative positionafter actuation by the lever I44 is delayed by a suitable time delaydevice 159 which is connected to the end of the lever I56 by link I60.Operatively secured for rotation with the ratchet wheel I48 is a switchoperating arm I6I which, when rotated through the requisite angle, willengage with the switch lever I62. The switch lever I62 is stationarilypivoted as at I63 and is biased to either one of two operative positionsby an overcenter spring I64.

'The other end of the lever I62 is provided with completing anenergizing circuit for a suitable alarm device indicated at I".

The ratchet wheel Ill isbiased to the reset position by means of asuitable spring I, this position being determined as by the engagementof lever I" with the stop I.

Whm the conveyor shaft is rotated in the fuel advancing orcounterclockwise direction the cam I" will strike the end of theoperating lever I to rotate the lever I in the clockwise direction. Thepin II! will merely slide downwardly in the slot Iii causing nooperation of the pawl M1,. The lever I will be returned to the normalIII of the arm I to rotate the latter lever in the counterclockwisedirection and actuate the pawl Il'l upwardly into engagement with theteeth of the ratchet wheel I. The hinged end I" of the lever I willsimultaneously engage with the end of the lever I to carry the springIS'I into engagement with the teeth of the ratchet wheel I". Under theimpulse of the pawl I 41 the ratchet wheel will be turned through apredetermined angle as measured by the spacing of the teeth. The wheelwill be retained in the actuated position for a predetermined time bythe spring II'I against the biasing force of the restoring spring I88.The spring I58 will tend to move the lever I58 and spring I51 to theinoperative position but due to the action of the time delay device I59,the return movement will be somewhat delayed.

The time delay device I" is so adjusted that it will retain the lever Iin the actuated position for a period, for example, twice as great asthe period of each reverse operation of the stoker driving motor. motorcontinues to alternate in the direction of rotation, the reversalsfollowing each other in relatively rapid succession, the ratchet wheelI48 will be progressively advanced until after a predetermined number ofreverse operations the switch operating arm ItI engages with the leverI62 to deenergize the motor circuit and close the alarm circuit. Afterthe motor is stopped, the time delay device I59 will drop out,permitting spring I58 to withdraw pawl I51 from the ratchet wheel. Underforce of spring I68 the ratchet wheel will be reset, arm IBI moving freeof the tripped switch operating lever I62 and into engagement with stopI69. However, if the stoker driving motor should succeed in breakingthrough the obstruction after a fewer number of reversals, and theconveyor shaft be operated in the forward direction for a period of timegreater than-the time for which the time delay device I" is set, thespring I51 will be withdrawn from'the ratchet wheel I48 and permit thespring I68 to return the ratchet wheel and the lever iii to the normalor reset position.

when the alarm circuit is closed indicating that the stoker motor hasbeen shut down by virtue of its inability to break through theobstruction, an attendant may correct the difficulty and reset theswitch arm It! to the operative position indicated.

Having described the principle of operation of my invention togetherwith the apparatus which apparatus shown is merely illustrative and thatthe invention may be carried out by other means.

As long as the stoker drivingv aasaus whatlclaimasnewanddesirstosecurebyLetters Patent of the United States. is;

i. Ina furnace stoker apparatus, the combination comprising a fuelconveyor, motor means connected to said conveyor for normally drivingsaid conveyor in the forward direction, said motor being automaticallyreversible in response to a predetermined torque exerted thereby to saidconveyor, means for limiting the reverse operation of said conveyor,means for counting the consecutive number of reverse'op'erations of saidconveyor, means for dg said motor upon a predetermined consecutivenumber of reverse operations of said conveyor being counted by saidcounting means, and means for auto matically resetting said countingmeans upon the consecutive number of reverse operations of said conveyorbeing less than said predetermined number.

2. In a furnace stoker apparatus, the combina- 20 tion comprising fueladvancing means, motor means connected for normally driving said fueladvancing means in the forward direction, means including said motor forcausing the direction of operation of said fuel advancing means to beautomatically reversed in response to a predetermined torque exertedthereto by said motor means. means for limiting the reverse operation ofsaid fuel advancing means, means responsive to a predeterminedconsecutive number of reverse operations of said fuel advancing meansfor causing the deenergization of said motor, and signal means adaptedto be energized upon the deenergization of said motor.

3. In a bulk material handling apparatus, the combination comprising amaterial conveyor, a motor connected for driving said conveyor normallyin the forward direction, means including said motor for automaticallyreversing the direction of operation of said conveyor in response tosaid conveyor encountering a predetermined resistance to operation inthe forward direction, means for limiting the reverse operation of saidconveyor and for causing said conveyor to be operated again in theforward direction, means responsive to a predetermined consecutivenumber of reverse operations of said conveyor for deenergizing saidmotor.

4. In a bulk material handling apparatus, material conveying means, amotor connected for normally driving said conveying means in the forwarddirection, torque responsive means for causing said motor to operate inthe reverse direction upon said conveying means encountering apredetermined resistance to operation in the forward direction, meansfor limiting the reverse operation of said motor, and means responsiveto a predetermined consecutive number of reverse operations of saidmotor for causing the deener- Bization thereof.

5. In a stoker, the combination with fuel advancing means, a motor fornormally driving said fuel advancing means in the forward direction,said motor having the characteristic that it automatically reverses itsdirection of rotation upon encountering a predetermined resistance tooperation in either direction, and ratchet means for limiting theoperation of said motor in the reverse direction as regards said fueladvancing matically reversible upon a predetermined torque being exertedthereby to said conveyor, means for stalling said conveyor after apredetermined period of reverse operation thereof so that said motor mayoperate in the forward direction again.

7. In combination, a stoker apparatus comprising a spiral screw fuelconveyor, a motor fast coupled to said conveyor screw, said motor beingautomatically reversible upon said conveyor screw encountering apredetermined resistance to operation in the one direction, and meansfor automatically limiting the operation of said conveyor screw in thereverse direction to a predetermined maximum number of revolutions.

8. In a stoker apparatus, the combination including fuel advancingmeans, a motor for driving said fuel advancing means, said motor beingarranged for normally driving said fuel advancing means in the forwarddirection, a torqueresponsive device between said motor and said fueladvancing means, a switch responsive to a predetermined actuation ofsaid torque responsive device for altering the electrical connectionsfor said motor for causing the reverse rotation thereof, and means forrestoring said switch to the normal condition a predetermined timefollowing the actuation thereof by said torque responsive device.

9. In a furnace stoker apparatus, the combination comprising a rotatablescrew type fuel conveyor, 'an electric motor coupled to said conveyorfor normally rotating same in the forward direction, means responsive toa predetermined abnormal resistance to rotation of said conveyor in theforward direction, switch means actuable by said means for changing theconnections of said motor to cause a reverse operation thereof, andmeans for restoring said switch to the previous condition apredetermined time following actuation thereof by said first means.

10. In a furnace stoker apparatus, the combination comprising fueladvancing meansflnotor means for normally driving said fuel advancingtransmitted by said motor to said conveyor, means actuable by said lastmentioned means for changing the connections of said motor to reversethe direction of operation thereof and said' material conveyor means,and means for 5 limiting the reverse operation of said motor andreconnecting said motor for operation in the forward direction.

12. In a bulk material handling apparatus, the combination comprising amaterial conveyor, means for driving said conveyor normally-in theforward direction, means for automatically causing said driving means toreverse the direction of operation of said conveyor means upon saidconveyor means encountering a predetermined abnormal resistance tooperation in the forward direction, and means for automatically causingsaid driving means to operate said conveyor means in the forwarddirection again following a predetermined reverse operation thereof.

13. In a furnace stoker, the combination comprising fuel advancingmeans, motor means connected for normally driving said fuel advancingmeans in the forward direction, means including said motor means forcausing the direction of 25 operation of said fuel advancing means to beautomatically reversed upon said fuel advancing means encountering apredetermined abnormal resistance to operation in the forward direction,and means for limiting the reverse operation of said fuel advancingmeans and causing said motor means to again drive said fuel advancingmeans in the forward direction.

14. In a stoker, the combination with fuel advancing means, a motor fordriving said fuel advancing means, said motor being arranged fornormally driving said fuel advancing means in the forward direction,means including said motor responsive to a predetermined abnormalresistance to forward operation of said fuel advancing means forreversing the direction of operation of said motor, and means forreconditioning said motor for operation in the forward direction after apredetermined period of operation in the reverse direction.

15. In a bulk material handling apparatus, the combination comprising amaterial conveyor, motor means connected to said conveyor for normallydriving said conveyor in the forward direction, means including saidmotor for causing the .direction of operation of said motor to beautomatically reversed upon said conveyor encountering a predeterminedresistance to operation in the forward direction, and means for limitingthe reverse operation of said motor and said conveyor. 55

WALTER O. LUM.

